1. Technical Field
The present invention relates to the field of data storage, and more particularly to an estimation technology in an error correction process of a flash memory.
2. Related Art
A storage unit in a flash memory device records logic information in the manner of injecting electrons in a floating gate, and at the same time the storage unit further determines logic saved in the floating gate through reading a threshold voltage. When having been rewritten many times, the device characteristics of the flash memory device attenuate, which shortens a programming time of the flash memory while extends an erasing time.
During the operation of a flash memory device, various parasitic effects occur at the same time, resulting in an error on data saved in the flash memory device. The most common error causes are: a programming disturbance, a read disturbance, a pass-through disturbance, and a floating gate coupling effect. During a programming operation of the flash memory device, a flash memory controller raises the voltage on a word line, which causes that an unexpected write action occurs in an adjacent storage unit on the word line, that is, a programming disturbance. In a bit line direction, a high pass-through voltage needs to be applied on storage units on one same bit line, so that to turn on the storage units on the flash memory. Repeated write operations result in unexpected write actions in the units on the bit line, that is, a pass-through disturbance. When the flash memory device undergoes many times of read operations, a flash memory array is turned on repeatedly, and electrons accumulate on trenches of storage units of the flash memory. When the accumulated electrons reach a write threshold value of the storage unit of the flash memory, an unexpected write operation occurs in the storage unit of the flash memory. Here, the disturbances affect the correctness of data saved in a solid-state hard disk, and severe disturbances further shorten the service life of the flash memory device. Also, the floating gate coupling effect also causes severe errors. As the flash memory process keeps developing, the density of devices keeps increasing, causing that a change of a threshold voltage on a floating gate of a single storage unit affects an adjacent unit, which results in an unexpected level shift and an error occurs. A voltage change of a floating gate of a storage unit in a flash memory array causes disturbances to floating gates of neighboring storage units, resulting in unexpected flipping of data saved in the neighboring storage units.
The disturbances and coupling effect in the flash memory device severely affects data saved in the flash memory. During practical use, an error correction algorithm is required to protect data saved in the flash memory. However, before a flash memory controller starts error correction by using advanced check code technologies such as a low-density check code, an error in a channel needs to be properly estimated. Therefore, the flash memory controller requires an error estimation technology for the flash memory.